1. Field of the Invention
The present invention relates to a control apparatus for an internal combustion engine, which may automatically stop a vehicle engine when the vehicle engine is not required to be driven during an operation and may quickly restart the vehicle engine when a re-acceleration request is made by a driver.
2. Description of the Related Art
In a vehicle using an internal combustion engine as a power source, the following technology for improving fuel efficiency is conventionally known. In an operating state at the time of, for example, deceleration where a driver does not press down an accelerator because the driver does not intend to drive the vehicle, a clutch provided to a torque converter of an automatic transmission is engaged to directly couple the engine and the automatic transmission while fuel supply to the engine is stopped.
For example, the following technology is disclosed. When the deceleration is performed by stopping the fuel supply to gradually reduce engine rpm, the clutch is disengaged at predetermined engine rpm higher than engine idling rpm. At the same time, the fuel supply is restarted to perform idle control, thereby preventing an engine stall (for example, see JP 58-166165 A).
As a technology of further improving the fuel efficiency as compared with the above-mentioned conventional technology, the following technology is disclosed. The fuel supply remains stopped unless the driver presses down the accelerator. On the other hand, when the driver requests re-acceleration by pressing down the accelerator, the clutch is engaged and the fuel supply is restarted. If the rotation of the engine is stopped at this time, the engine is restarted by a starter so as to prevent engine idling, which does not contribute to drive of the vehicle, as much as possible (for example, see JP 08-189395 A).
Further, the following technology of restarting the engine is also disclosed. According to the technology, when the amount of pressing of a brake becomes small in a fuel-supply stop state during deceleration in a hybrid vehicle, it is judged that the driver has an intention to accelerate the vehicle. Then, the clutch is engaged to couple the engine and a drive train to each other. As a result, the engine is cranked by an inertia torque of the drive train while the fuel supply is started. In this manner, the engine is restarted (for example, see JP 2002-144921 A).
In the case where the method described in JP 08-189395 A is employed, however, if the accelerator is pressed down again after the engine rpm becomes equal to or lower than engine rpm at which the clutch is disengaged during the deceleration, there is a fear of generating a shock at the moment of engagement of the clutch. Moreover, the engine is restarted using the starter in the case where the rotation of the engine is stopped, and hence there is a fear in that gear meshing noise is generated in the starter each time the accelerator is pressed down during the deceleration.
Further, in the case where the method described in JP 2002-144921 A is employed, there is a fear of generating the shock at the moment of engagement of the clutch because the clutch is directly engaged to rotate the engine which was in a stop state until then. Moreover, when a vehicle speed is low, rpm is low on a drive side. Therefore, the engine rpm may not be increased to sufficient cranking rpm through an intermediation of the clutch. The cranking is required to be performed using the motor, and hence there is a fear of consuming extra electric power.